Certain types of catalysts are utilized in industrial, commercial or consumer applications to reduce the emission of unburned hydrocarbons (“HC”), volatile organic compounds (“VOC”), and/or nitrogen compounds such as nitrous oxides. One such group of catalysts is generally known as washcoat catalysts, which may be utilized, for example, in automobile catalytic converters or for reducing nitrous oxide in emissions from gas-fired turbines. Typically, washcoat catalysts are formed of an inert substrate or carrier (the terms “substrate” and “carrier” being used interchangeably herein), which is coated with a catalytic material in an immersion process.
The inert substrates or carriers may be formed, for example, of suitable materials such as ceramic, zeolite, or metal. Particularly useful substrates include a ceramic or zeolite materials formed into shaped blocks having through-holes of selected design. This type of substrate is commonly referred to as a “honeycomb.” Other useful substrates are metallic substrates formed as a layered or corrugated structure. Typically, the inert substrates are coated with a combination of catalytic materials, as well as a glue or binder that may be used to facilitate the application and retention of the catalytic materials on the substrate. In such instances, silica-based or acrylate glues binders are common.
In use, washcoat catalysts tend to lose their effectiveness over time. This degeneration can be due to one or more factors, including clogging, poisoning by metals such as sodium, other types of catalytic poisoning, or the reaction of catalytic materials with other substances found in emissions. In the past, degenerated washcoat catalysts were typically discarded, including the underlying inert substrate.